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Software Quality EngineeringCS410

Class 2

Software Process Models

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SW Process Models

• A process model is:– Methodology - 1) A body of methods, rules,

and postulates (accepted theory or statement) employed by a discipline. 2) A particular procedure or set of procedures. (Webster’s 9th Collegiate Dictionary 1988)

– Life Cycle - synonym for methodology

• A process model is not:– Method

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SW Process Models (cont.)

• Method - A step-by-step technical approach for performing one or more of the major activities identified in an overall methodology for software development.

• For example: Structured analysis and Object-Oriented analysis are both methods for carrying out the analysis phase of a software development project.

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SW Process Models (cont.)

• Common Process Models– Waterfall– Prototyping

• Rapid Throwaway

• Evolutionary

– Spiral– Iterative– Object-Oriented– Cleanroom

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Waterfall• First attempt at controlling SW development.

• Encourages requirements gathering, ordered stages, and documentation

• Divide and conquer approach

• Clearly defined stages– Requirements– Design– Code– Test– Maintenance

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Waterfall (cont.)• Deliverables at each stage

• Entry/Exit criteria for each stage

• Feedback between stages

• Emphasis on documents

• Waterfall model– Figure 1.2 p. 6– Figure 2.1 p. 15

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Waterfall (cont.)

• Requirements Gathering/Analysis Stage– Meetings with customers– Feedback forms– Trade shows– Conferences– Internal requirements (ISO, etc.)– Requirements document is deliverable

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Waterfall (cont.)• Architectural Design Stage

– Ensure operational consistency with product line(s), and standards

– Architecture:• The structure of the components of a

program/system, their relationships, and principles and guidelines governing their design and evolution over time.

• Gross organization and control structure

• Protocols for communication, synchronization, and data access

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Waterfall Sample

Source: MS Project

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High-Level Design (HLD)• Develop external functions and interfaces

– User interfaces– Application Programming Interface (API)– System Interfaces– Inter-component Interfaces– Data structures

• Design control structure

• Ensure functional requirements are met

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High-Level Design (HLD)

• Ensure components fit into system/product structure (feedback to Architecture stage)

• Ensure component design is complete

• Ensure external functions can be accomplished (feedback to Requirements stage)

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Low Level Design (LLD)

• Identify parts, modules, macros, include files, etc. that will be written or changed

• Finalize detail level of design

• Verify changes in HLD (feedback to HLD)

• Verify correctness/completeness of HLD (feedback to HLD)

• Create component test plans (from requirements and design specs)

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Code Stage

• Transform LLD into coded parts– Code modules, macros, includes, messages etc.– Create component test cases– Verify design (feedback to LLD and HLD)

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Unit Test Stage

• Verify code against LLD/HLD

• Execute all new and/or changed code– Branch coverage– Statement coverage– Logic coverage

• Verify error messages, error handling, return codes, input parameters

• May require stubs and drivers

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Component Test• Test the combined software parts that make

up a component after the parts have been integrated into a library (Configuration Management - CM)

• Objective is to test:– External user interfaces (do they meet

requirements)– Inter-component interfaces– APIs

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Component Test– Functionality– Intra-component (module) interfaces– Error recovery– Messages– Concurrency (multi-tasking)– Shared Resources– Existing functionality (regression)

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System-Level Test• Four portions

– System Test, Regression Test, Performance, Usability

• System Test– Test concurrency– Stress test– Test overall system stability and completeness

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System-Level Test• Regression Test

– Test original (unchanged) functions

• Performance Test– Validate performance of system/product against

requirements– Record performance metrics– Establish baselines (I.e. benchmark)

• Usability Test– Test for usability requirements

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Goal of Testing

• Verification– Verify that the system/product we built meets

all of the user requirements for usability, performance, reliability, etc. Verify that the intrinsic quality is high and that standards have been met.

• Validation– Validate that the requirements that drove the

process were correct.

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Waterfall (cont.)• Advantages:

– Better than an adhoc approach– Process, requirements, entry/exit criteria, designs

are all documented

• Disadvantages:– Assumption that requirements will not change– Heavy emphasis on documents– Performance problems detected late in cycle– Rework is costly– Feedback is not formalized

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Prototyping Model

• Designed to deal with changing or unknown customer requirements.

• A prototype is a partial implementation of the product expressed either logically or physically with all external interfaces presented.

• Prototype is ‘used’ by customer to help develop requirements

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Prototyping Model

• Prototyping steps:– Requirements gathering and analysis– Quick design– Build prototype– Customer evaluation– Refinement of design and prototype (and

requirements)– Decision: Iterate or accept

• Figure 2.2 p. 20

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Prototyping Model

• Key to success: Quick turnaround and inexpensive

• Throwaway Prototyping– Good for:

• High-risk projects

• Complex problems

• Performance concerns

– “quick and dirty” approach– Once customer satisfied, then development of

“real thing” begins

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Prototyping Model

• Evolutionary Prototyping– Some requirements are known– Each iteration evolves (refines) prototype– May or may not become final product

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Prototyping Model• Advantages

– Good for interface design– Good when requirements/problem not understood– Problems detected/corrected early– Requirements refined and validated

• Disadvantages– Hard to know when to stop– Could be costly– Tempting to use prototype as product (in

throwaway approach)

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Spiral Model

• Refinement of the Waterfall Model

• Focus is on Risk Management and prototyping

• Idea: A sequence of steps (cycle) is executed for each level of elaboration. A risk analysis is performed in each cycle.

• Prototyping is applied to the high-risk areas

• Figure 2.3 p. 23

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Spiral Model

• Advantages– Risk Driven– Incorporates prototypes– May encourage reuse– Eliminates bad alternatives early– Incorporates maintenance– Allows for quality objectives to be incorporated

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Spiral Model

• Disadvantages– Immature process– Looser checkpoints (compared to Waterfall

with the documents and entry/exit criteria)– Requires good understanding of Risk-Analysis

and good risk driven decisions

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Iterative Model

• Idea: Start with subset of requirements and develop a subset of the product to meet these requirements. After analysis of product, iteration is done and process is repeated with new requirement subset.

• Goal: Provide a system/product to user that meets evolving customer needs with improved design based on feedback and learning.

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Iterative Model

• Combination of Waterfall and Prototyping– Non-iterative portion like Waterfall Model– Iterative portion like Prototyping Model

• Similar to Spiral model

• Key elements– Test suite developed at each iteration– Each iteration is verified and validated

• Figure 2.4 p. 26

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Iterative Model

• Advantages– Complexity broken down– Problems detected early– Allows evolution of requirements– Smaller development teams

• Disadvantages– Risk Analysis not formalized– Less parallelism

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Object-Oriented Model

• Paradigm shift away from data and control, to objects which incorporate both data and methods.

• Eight step process (Branson and Herness)

• 1. Model the essential system– User view– Essential activities– Identify essential model

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Object-Oriented Model

• 2. Derive candidate essential classes– Class and method selection based on the essential

model identified in step 1

• 3. Constrain the essential model– Model must be constrained to work within the

limits of the target implementation environment

• 4. Derive additional classes– Derive classes/methods specific to

implementation environment (I.e. environmentals)

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Object-Oriented Model

• 5. Synthesize classes– Organize classes into a class hierarchy

• 6. Define interfaces– Interfaces and class definitions are written

based on the class hierarchy

• 7. Complete design– Complete design to include logic, system

interactions, method invocations

• 8. Implement solution

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Object-Oriented Model

• Phases– Analysis: steps 1-2– Design: steps 3-6 (can be iterated)– Implementation: steps 7-8

• Reviews are performed to enhance control of the project

• Prototypes can be used for the essential model

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Object-Oriented Model• Advantages

– OO may promote higher reuse levels– Promising new technology– Works well on small projects

• Disadvantages– No commonly recognized OO model– Training– Paradigm shifts– Process needs to mature

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Cleanroom Model

• Statistical (mathematical) based

• Based on correctness verification and incremental development

• Developers must ‘prove’ designs/code rather than test designs/code

• Statistical testing replaces unit testing

• Figure 2.5 p. 33

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Cleanroom Model

• Advantages– Developers are motivated to “get it right the

first time” - no unit test safety net– Promises significant quality improvements

• Disadvantages– All (statistical) testing is based on expected use– Learning curve, training requirements– Limited use in industry– Questions regarding scalability

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Pop QuizIn 27 words or less:

• Define:• CMM• Defect Rate• ISO 9000• Spiral Model• DPP

• What are the advantages of doing a Malcolm Baldrige Quality assessment?

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Review

• CMM

• Waterfall Model– High Level vs Low Level– Unit vs Component Testing

• Prototyping

• Spiral Model

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Software Quality EngineeringCS410

Class 3

DPP, Process Maturity,

Quality Standards

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Defect Prevention Process• A process for continually improving a

software development process

• It is not a software methodology or model

• Three main steps– Analyze existing defects or errors to trace the

root cause– Suggest preventative actions to eliminate the

defect root cause– Implement the preventative actions

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Defect Prevention Process• Four key elements:

– Causal analysis meeting - analyze defects for each stage of the development process, identify root cause, identify prevention actions, look for trends

– Action team - prioritize and implement action items

– Stage kickoff meeting - level setting, emphasis on quality improvement through action items and process improvements, pitfalls identified and discussed

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Defect Prevention Process– Action tracking and data collecting - record all

problems, root causes, and actions (and action status)

• DPP should be done at every stage (unlike postmortem which is at end of entire project)

• DPP addresses ISO 9000 corrective action

• DPP can be used with any development model, but may be more effective with some (I.e. iterative)

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Process Maturity Frameworksand Quality Standards

• Attempt to measure implementation maturity of a software development process (I.e. how well is it executed), and analyze the quality management systems in place

• Capability Maturity Model (CMM)• Software Productivity Research (SPR) assessment• Malcolm Baldrige process/assessment• ISO 9000

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Capability Maturity Model• Developed by Software Engineering Institute

(SEI) at Carnegie-Mellon Univ.

• A (process) maturity assessment framework

• Based on 85 item questionnaire

• Five levels of process maturity (p. 40-41)1. Initial

2. Repeatable

3. Defined

4. Managed

5. Optimizing

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SPR Assessment(p. 43)

• Developed by Software Productivity Research (SPR) Inc.

• Based on 400 question questionnaire

• Questions are rated 1-5, and overall process rating is expressed on 1-5 scale

• Questions focus on – Strategic corporate issues– Tactical project issues

• Quality, Productivity, Customer satisfaction

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Malcolm Baldrige Assessment• Malcolm Baldrige National Quality Award

(MBNQA) - “most prestigious quality award in the United States”

• Seven categories of examination criteria– Leadership

– Information and analysis

– Strategic quality planning

– Human resource utilization

– Quality assurance of products and service

– Quality results

– Customer Satisfaction

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Malcolm Baldrige Assessment• 28 examination items• 1000 possible points awarded• Scoring is based on three evaluation dimensions

– Approach - methods used to address the item

– Deployment - extent to which the approach is applied

– Results - outcomes and effects

• Winners need to score 70% or better to be considered

• Evaluation feedback/suggestions are provided regardless of score

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ISO 9000

• International Organization for Standards– (standards 9000, 9001, 9002, 9003)

• A set of standards for quality assurance

• Heavy influence in Europe

• Focus– Process quality– Process Implementation

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ISO 9000

• Goal - to achieve certification/registration

• Formal Audit performed

• Trial-runs can be performed by independent consulting firms - goal is to get feedback and suggestions

• First time failures 60% - 70%

• 20 elements to guideline (p. 46)

• Heavy emphasis on documentation (p. 47)

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ISO 9000

• ISO Focus on metrics (statistical techniques)

• Product Metrics Goals– Collect data and report values on regular basis

– Identify current metric performance level

– Take action if performance level is unacceptable

– Establish improvement goals

• Process Metrics Goals– Determine if quality objectives are being met

– Track adherence to process model and methods

– Track defect prevention effectiveness